Supporting information

Anisotropic layer-by-layer carbon nanotubes/boron nitride/rubber

composite and its application in electromagnetic shielding

Yanhu Zhan1, Emanuele Lago2,3, Chiara Santillo4, Antonio Esaú Del Río Castillo2,

Shuai Hao5, Giovanna G. Buonocore4, Zhenming Chen6, Hesheng Xia5, Marino

Lavorgna4*, Francesco Bonaccorso2,7

1. School of Materials Science and Engineering, Liaocheng University, Liaocheng

252000, China

2. Graphene Labs, Italian Institute of Technology, via Morego 30, 16163 Genoa,

Italy

3. Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova,

via Dodecaneso 31, 16146 Genoa, Italy

4. Institute of Polymers, Composites and Biomaterials, National Research Council,

P.le Fermi, 1-80055 Portici, NA, Italy.

5. State Key Laboratory of Polymer Materials Engineering, Polymer Research

Institute, Sichuan University, Chengdu 610065, China

6. Guangxi Key Laboratory of Calcium Carbonate Resources Comprehensive

Utilization, Hezhou University, Hezhou, City 542899, China.

7. BeDimensional S.p.a. Via Albisola 121, Genova 16163, Italy

* E-mail address: marino.lavorgna@cnr.it

Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2020

1. hBN and few-layers graphene characterization.1.1 Transmission electron microscopy. The hBN and the graphene samples are diluted 1:50, in N-methyl-2-pyrrolidone, and stored under vacuum at room temperature. TEM images are taken by using a JEOL JEM-1011 transmission electron microscope, operated at an acceleration voltage of 100 kV.

1.2 Atomic Force microscopy. The dispersions are diluted 1:30 in NMP. 100 mL of the dilutions are drop-cast onto Si/SiO2 wafers and dried at 50 °C overnight. AFM images are acquired with a Bruker Innova AFM in tapping mode using silicon probes (frequency = 300 kHz, spring constant = 40 N m-1). The thickness statistics are analysed by measuring B100 flakes from the AFM images. Statistical distributions are fitted with log-normal curves. Statistical analyses are performed in WSxM Beta 4.0 software.

1.3 Raman spectroscopy. The as-prepared dispersions are diluted 1:30 in NMP and drop cast onto a Si wafer (LDB Technologies Ltd) covered with 300 nm thermally grown SiO2. The bulk materials are analysed in the powder form. Raman measurements are carried out by using a Renishaw inVia spectrometer using a 50x objective (numerical aperture 0.75), and a laser with a wavelength of 514.5 nm with an incident power of mW. A total of 30 points per sample are measured to perform the statistical analysis. OriginPro 2016 is used to perform the deconvolution and statistics.

Figure S1. Characterisation of the exfoliated hBN and graphite. a) A TEM image of an exfoliated hBN flake, the inset shows the size distribution with a mode of 360 nm. b) AFM image of exfoliated hBN flakes, the inset shows the thickness distribution with a mode of 2.4 nm. c) Raman spectroscopy comparing the characteristic E2g peak

of bulk and exfoliated hBN. d) The TEM image of exfoliated few-layers graphene flakes, the inset shows the size distribution with a mode of 460 nm. b) AFM image of exfoliated flakes, the inset shows the thickness distribution with a mode of 1.6 nm. c) Raman spectroscopy comparing the characteristic D, G and 2D bands of bulk and exfoliated graphite flakes.

2 Polymer composites characterization.

Table S1. The experimental formula of composites latex for realizing the CNTs and hBN composite layers, the mass of HMR 10 latex was 4.23 g and H2O was 38 g.

Filler* content(phr)

Filler* content (wt%)

Filler* (g) CTAB (g)

2 1.96 0.05 0.054 3.85 0.1 0.16 5.66 0.15 0.158 7.41 0.2 0.212 10.71 0.3 0.316 13.79 0.4 0.4

*Filler refers to CNTs and hBN

Table S2. Thermal and electrical conductivity and EMI SE of layered composites with graphene having thickness of 1.4 mm.

Thermal conductivity (Wm-1K-1)

Electrical conductivity

(S cm-1)

EMI SE (dB)

8-R(graphene4C4)B8 0.33 0.234 15.028-R(graphene8)B8 0.35 3.98×10-5 11.57

Table S3. EMI SE in 8.2-12.4 GHz range for the presented NR/CNT composites and

the layered rubber composites prepared in this work.

SampleThickness

(mm)CNT content

(wt%)SE

(dB)

specific EMI SE

(dB mm-1)Ref.

NR/CNT6.40 foam 1.3 6.40 33.74 25.95 [S1]CNT/NR 1.5 5.0 33.3 22.2 [S2]

SBR/CNT 5 9.09 35.06 7.01 [S3]BR/CNT 1 7.41 13 13 [S4]

NR/ENR/CB 4 23.08 23.58 5.90 [S5]TPNR/Fe3O4 9 12 25.52 2.84 [S6]NR/CB/silica 2.83 41.18 16.06 5.67 [S7]

tire rubber/CNT 2.6 2 (+13.1 CB) 36.8 14.15 [S8]

NR/Fe3O4@graphene 1.6 4.50 (graphene) +20.48 (Fe3O4)

32.9 20.56 [S9]

28.87# 20.62#

8-RC8B12 1.4 7.4 (+10.7 wt% hBN) 31.38## 22.41##

This work

29.93# 21.38#

8-RC8B16 1.4 7.4 (+13.8 wt% hBN) 32.52## 23.23##

This work

# electromagnetic waves entering from NR/CNT layer## electromagnetic waves entering from NR/hBN layer

Table S4. The electric heating behaviour of polymer-based composites with lengths of 10 mm and wide of 3 mm.

Sample Filler content

Thickness (mm)

Potential (V)

Steady-state temperature

(oC)Ref

Epoxy/graphene 10 wt% 0.1 30 126 [S10]Epoxy/graphene/CNT 10 wt% 0.1 20 160 [S11]

Epoxy/graphene 10wt% 0.1 20 40 [S11]PDMS/CNT/graphene 10wt% - 20 ~55 [S12]PDMS/graphene-90/10 10wt% - 20 ~25 [S12]

8-RC4B8

4phr CNT8phr hBN

1.4 5 165.4 This work

8-RC8B12

8phr CNT12phr hBN

1.4 2.5 103.3 This work

Figure S2. SEM image of 8-RC8B12 sample (a) and 8-RC2B8 sample before (b) and

after (c) bending cycles; SEM images of the tensile fracture surface of the 8-RC2B8

sample (d) (◆: NR/hBN layer; ★: NR/CNT layer). The arrows in the images point to

the position of the interface between two adjacent layers.

Figure S3. Energy dispersive spectrum for 8-RC8B8 composite.

Figure S4. Specific heat capacity of RCB composites at 25 °C

Figure S5. Electrical resistance measurement of 8-RC8B12 composite in through-plane

direction (a) and in-plane direction (b); and the image of electronic circuit design (c).

Figure S6. Fourier transform infrared spectra of CTAB, NR, NR/CNT layer and

NR/hBN layer of the sample 8-RC8B12: a) from 400 cm-1 to 4000 cm-1; b) from

2600 cm-1 to 3400 cm-1; c) from 1200 cm-1 to 1700 cm-1. d) FTIR spectra of

CTAB, NR/CNT layer of the sample 8-RC8B8 and sample 8-RC8B12.

The reduction of the electrical conductivity for RCB composites by increasing the

amount of hBN can be ascribed to the effect of cetyltrimethylammonium bromide

(CTAB) surfactant, which adhering onto the surface of CNT limits the filler-filler

contacts and affects the conductive pathways. In details, the reduction of the electrical

conductivity is attributed to the CTAB content that remains in NR/CNT layers during

the filtration process. Indeed, since the NR/CNT dispersion is always filtered as first,

during filtration, the surfactant coming from the NR/hBN dispersions (the ratio

between the surfactant and the filler is fixed equal to 1:1) permeates into the NR/CNT

layers and deposits onto the surface of the CNTs contributing to reduce the tunnelling

electron transport. The higher is the hBN content, the higher is the content of

surfactants that permeates through the CNTs layers and potentially adhere to the

CNTs surfaces.

To confirm the aforementioned discussion, FTIR analyses have been performed on

the two layers of 8-RC8B12 and 8-RC8B8 composites, i.e., the first layer with only

CNTs (NR/CNT layer) and the last layer containing hBN (NR/hBN layer). The FTIR

results are shown in Figure S6. The pristine NR and CTAB present adsorption bands

in a similar region. In fact, ATR-FTIR spectrum of the NR exhibits characteristic

absorption bands of CH3 asymmetric, CH2 asymmetric and CH2 symmetric stretching

at 2961, 2920 and 2853 cm-1, respectively. The bands at 1446 cm-1 and 1377 cm-1 are

assigned to the CH3 and CH2 deformations, respectively, and the band at 837 cm-1 is

related to the CH out-of-plane deformation. The spectrum of CTAB shows two sharp

peaks at 2918 and 2850 cm-1 related to the C-H stretching vibration of methyl and

methylene groups. The peaks at 1487, 1473, 1463 and 1431 cm-1 correspond to

symmetric and asymmetric C-H scissoring vibrations of N+-CH3 moiety, while the

bands at 960 cm-1 are related to the C-N+ stretching,demonstrating the presence of

CTAB in the samples.

Although the NR and CTAB show adsorption bands in similar regions and the

quantity of CTAB, which remain in the RCB samples, is very low after filtration, it is

possible to observe some differences by comparing FTIR spectra of the NR/CNT and

NR/hBN layers for the same composites and also by comparing different composites.

The spectrum of the NR/hBN layer shows the adsorption bands at 2961, 2920 and

2853 cm-1 with the same relative intensities of those observed in the spectrum of the

pure NR. Instead, different relative intensities of these three peaks are observed in the

spectrum of the NR/CNT layer. In particular, the peak at 2918 cm-1 is more intense

than the peak at 2850 cm-1.Both peaks are sharper than in the case of the same

adsorption bands shown by the NR and the NR/hBN layer. The increase of the peak’s

intensity at 2918 cm-1 can be attributed to the presence of the surfactant.

Moreover, in the spectrum of the NR/CNT layers is observed the appearance of a

shoulder at 1486 cm-1 related to the (-N+-CH3) moieties of the CTAB, which are not

present in the spectra of both the pristine NR and the NR/hBN layer (that means the

CTAB is leached from the NR/hBN layer but it remains onto the surface of CNTs).

Therefore, from FTIR analysis it is possible to conclude that the quantity of CTAB in

the NR/CNT layers is higher than that present in the NR/hBN layers.

At the same time, the FTIR results confirm that the quantity of CTAB presents in the

layer with CNTs depends on the content of surfactant in the hBN layer. The higher is

the content of CTAB in the hBN layer, the higher is the content which is left adhering

onto the CNTs surfaces. In particular, Figure S6d reports a comparison between

spectra of NR/CNT layers of samples with different content of hBN. It is evident that

the intensity of the shoulder at 1486 cm-1 is higher in the spectrum of the NR/CNT

layer of the sample 8-RC8B12 than in the spectrum of the NR/CNT layer of the sample

8-RC8B8. This demonstrates that the quantity of CTAB in the layers containing CNTs

increases with the amount of hBN filler in the RCB composites, and thus it

contributes to reducing the electrical conductivity values of materials containing 8 phr

of CNT with content of hBN higher than 8 phr.

Figure S7. Effect of filler content on the density of RCB composites

Figure S8. Effective absorbance of 8-RCxBy composites (solid symbol: EM waves

enter into samples from NR/CNT layer; hollow symbol: EM waves enter into samples

from NR/hBN layer)

Figure S9. Schematic illustration of surface temperature measured by IR camera

under fixed voltage.

100 200 300 400 500 600 7000

20

40

60

80

100 NR 8-RC8B12

8-RC8B16

Wei

ght (

%)

Temperature (°C)

Figure S10. Thermogravimetric curves of NR and RCB composites

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